Finishing a Graded Garage

Hi all. I am finishing a garage area wherein the concrete floor is graded for drainage at an angle of about 6'' over a 20' run. I'd like to level this floor. My proposed method for doing so is to apply a vapor barrier, followed by joists or sleepers ripped at an angle commensurate with the floor angle so that one end would be six inches higher than the other creating a level surface, then a ply sub-floor. Anybody ever try this or have an opinion on my plan? Also curious if you would allow the sleepers to float or anchor them to the concrete floor to prevent slipping. Thanks. -Aaron

The house is in Florida, quite near the beach, and this house was essentially built on stilts (really filled concrete block pillars). The space below was graded presumably for easy drainage as a carport or garage. Half the lower floor was closed in before I bought the house, but it is not connected to the living area upstairs, so you have to go outside, walk down exterior stairs to get to that downstairs living area or to get to my laundry. I want to close in the other half of the downstairs to add an interior stair to make the house a cohesive whole. Another option, and perhaps a better one, as eluded to in post #2, would be to drill some holes in the concrete floor, add rebar, and simply pour new concrete atop the existing floor to level. I like the idea of this as I want to tile down there anyway and this would be a fine subfloor for tile, I'm just leery of adding new concrete to old. The floor is in beautiful shape, no cracks, perfectly smooth- just too steeply graded for a living area. Thanks- Aaron

I just checked the grade to confirm my numbers and I was a bit off. The dimensions of the area to be regraded are 18'x14' with a grade of 7 1/2'' over the 18' run. By my calculations, (and they could be wrong), that's about 3 yards of concrete.

I just checked the grade to confirm my numbers and I was a bit off. The dimensions of the area to be regraded are 18'x14' with a grade of 7 1/2'' over the 18' run. By my calculations, (and they could be wrong), that's about 3 yards of concrete.

I got that by multiplying length times width times depth. In this case I multiplied 14' x 18' x 7.5 / 12 (to get to ft.) / 2 (to account for the slope which is the shape of a right triangle) / 27 (to get to cu. yards) and came up with 3. That's 7 1/2'' at it's deepest to 0'' at the other end where it will meet level concrete. I've never done this before, did I do it incorrectly?